Currently, maintaining image quality during conjugate change is most frequently achieved through careful lens design with the multiconfiguration optimizing method and physical shifts of the lenses within the system such that the system remains in focus. However, in applications with operational limitations, such as endoscopy where the space available cannot allow for moving parts, the lens system needs to be designed such that the system is in focus over a wide range of conjugates. A lens design method that is integrable into existing commercial lens design software is presented. This method derives and maintains an optimal condition for astigmatism and distortion to control and reduce the overall aberration variation during the conjugate change, and extends the depth of field of the system. A side-by-side lens design comparison between the method illustrated in this study and the conventional lens design method commonly employed by designers of zoom lenses is also presented and is demonstrated to produce better results in designing conjugate change optical systems.